The present invention relates to a semi-mounted plough control system for an agricultural tractor.
A semi-mounted plough has a support wheel at the center or at the far end on which the plough is supported via a hydraulic cylinder for height adjustment. This means that the height of the near end of the plough, which is mounted on a tractor 3-point linkage and the height of the far end of the plough are controlled by separate hydraulic lines.
It is known, to provide an electronic control system to co-ordinate the lifting and lowering of each end of a semi-mounted plough. Such a system is described fully in U.S. Pat. No. 5,261,495, which is incorporated herein by reference. Using this system, the front end of the plough is caused to enter work before the rear end of the plough so that the diagonally arranged individual ploughshares enter work in the same plane, perpendicular to the direction of travel of the tractor. This makes for even boundaries to the worked area of a field. The same type of control is applied on removing the plough from work.
In the above system, a value is inputted to the control system before ploughing commences which is representative of the length of the plough. The control system uses this value together with the sensed speed of the tractor to determine a time delay between the lowering of the front and rear of the plough into work and a similar time delay between removal of the front and rear of the plough from work. Once the value for the implement length has been input into the control system, it is often not necessary to adjust the settings on the control unit during ploughing. In fact, there are alternative systems which are associated with a particular plough rather than being part of a tractor based control system which will have the implement length value fixed at an appropriate value.
A problem arises, however, when the direction of the furrows is not perpendicular to the field boundaries at each end of the furrows. In this event, to create a neat boundary to the worked area, it is necessary to cause the individual ploughshares to enter work at spaced apart locations with respect to the direction of travel of the tractor to follow the boundary line of the field. It is possible to do this using the known control system, by inputting an adjusted value for the implement length at the beginning of the ploughing operation. This value would be worked out by the operator based on experience so that it takes into account both the actual length of the plough and also the geometry of the field. The problem with this, however, is that this value for "plough length" is only appropriate for one end of the worked area of the field, unless the field boundaries are parallel. Even where the boundaries are parallel, the appropriate "plough length" will be different for entry and exit from work at one end of the field, where a reversible plough is used. Since reversible ploughs are used almost universally now, this means that the "plough length" value needs to be adjusted on every headland turn, at a time when the operator is also having to make a tight turn, change gear and operate lifting/lowering of the linkage. It is difficult for the operator to perform all these functions satisfactorily and this also makes for tiring work because this series of operations has to be performed on every headland turn.